During the past century the plastics industry has brought into use a broad and varied range of wonder materials which are employed in nearly every major industry including the electrical, automotive, steel, railway, food-packaging, printing and textile industries. In all of these technological fields the by-words for low cost and mass production capability are "made of plastic". This wide use has resulted because of the wear resistance, flexibility, strength, resistance to water and acids, lightweight and low cost properties of these materials and also because of the many ways in which it may be worked or fabricated including, inter alia, molding, extrusion, laminating, casting and calendering.
Because of this universal popularity of plastic materials including their resistance to rust, rot and breaking down again into their natural forms, the disposal of worn-out plastic materials has become a challenging problem.
Plastics are a family of synthetic materials composed of extremely large molecules called polymers, which are synthesized from simpler molecules called monomers. The overall properties of a plastic are a result of the combined properties of all its molecules, such as their different sizes, their chemical structure and shape, and their ability to crystalize. Furthermore, the properties of plastic materials can be altered by mixing them with additives. Additives are mixed or compounded with the polymer to improve its processing characteristics and produce other desirable properties. The resulting product is then called compound or resin. Resin is a general term that also denotes additive-free polymer.
Polymers that soften when heated and can be shaped if heat and pressure are applied are called thermoplastics. Polymers that soften and can be shaped only during the first heating cycle and cannot be reformed are called thermosetting plastics. Since thermosetting plastics are not easily recycled, this invention is directed to thermoplastics, which today represent about 80 percent of all plastics. Some coatings and adhesives are thermoplastic, but they are impossible to recycle. When they are excluded, the percent of potentially recyclable thermoplastics remaining is 75 percent of all plastics, or approximately 15 billion pounds in 1970, i.e. five major thermoplastics; low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene, styrene polymers, and polyvinylchloride (PVC). These five represent 89 percent of all thermoplastics (excluding coatings and adhesives).
The term scrap plastic denotes all scrap that has value and is recycled, such as the scrap generated during the manufacture of resin and plastic items. This scrap may be in the form of contaminated compound, film trimmings, strands, or large chunks of plastic from the molding machinery.
Nuisance plastic is used to denote that portion of plastics production that has no value and is usually found in the disposal area. For example, the consumer generates nuisance plastic when he disposes of his spent plastic products, and, if the manufacturer cannot use his scrap, it also becomes nuisance plastic.
Nuisance plastics heretofore had no value. The consumer disposes of a plastic item after a certain lapse of time, which is the service life of the product. For example, packaging, novelties, disposables, etc., have a short service life (less than 1 year). Other items, such as furniture, sporting goods, and luggage have estimated service lives of 6 to 10 years, and products such as instruments, hardware, and various machinery can serve for 11 to 20 years. It is those plastic items having a short service life that are the major source of nuisance plastics in the disposal site today and, therefore, recycling of these should be promoted.
Packaging--a short service life product-- is the major source of nuisance plastic. The plastic derived from packaging wastes generated by the five major thermoplastics accounted for 60 percent (weight) of the 6.5 billion pounds of all nuisance plastic in the disposal area in 1970. Assuming that conditions and technology remain unchanged, it's estimated that plastic packaging wastes will still dominate the disposal area in 1980 when they will be equivalent to 10 billion pounds or 54 percent of all nuisance plastics. If the plastic beverage container becomes a reality, plastic packaging wastes could increase to 12 billion pounds by 1980, or almost three times the 1970 volume. This would represent about 59 percent of all nuisance plastic in the disposal area.
As a general rule, scrap plastic has to be used in an end application having broader specification requirements than the product yielding the scrap. The fabrication of bottles, film of high quality, and certain coatings requires resin with tightly controlled specifications. In contrast, many plastic products made by molding or extrusion, whether they are housewares or pipe, use resin having a relatively broader specification range. Thus, scrap from plastic bottles, though difficult to recycle as bottles, can be used for pipe, siding, and a variety of structural products.
Scrap is being used to make a number of products today, and it is believed that if more secondary resin is made available at a sufficiently low price, new applications will develop.